Could cannabidiol help prevent tumors and other cancers before they grow? A 2012 study showed that animals treated with CBD were significantly less likely to develop colon cancer after being induced with carcinogens in a laboratory.[187] Several studies had already shown that THC prevents tumors and reduces them, including one in 1996 on animal models that found that it decreased the incidence of both benign and hepatic adenoma tumors.[188] In 2015, scientists analyzed the medical records of over eighty-four thousand male patients in California and found that those who used cannabis, but not tobacco, had a rate of bladder cancer that was 45 percent below the norm.[189] Topical products can be used to treat and prevent skin cancers. Continuing research is focused on the best ratio of CBD to THC and the most effective dose level in cancer prevention and treatment.